Spray nozzles are well known devices for producing controlled sprays of liquids for applications such as paint spraying, crop spraying to dispense fertilizer and insecticide, industrial washing and chemical treatment. For most applications it is essential for a spray nozzle to produce an evenly distributed spray of uniform liquid particles in a predetermined spray pattern.
In most cases the spray pattern consists of fine droplets created by forcing liquid into the nozzle through a large orifice and out of the nozzle through a smaller discharge orifice or plurality of smaller discharge orifices. The finer the droplets required, the smaller the size of the discharge orifice. The discharge orifices in known spray nozzles are usually outlet openings of a static nature and preset dimensions, e.g. holes drilled or molded into the ends of nozzle members. The outlet openings or holes, being of small size, have a tendency to block frequently with particles of dirt, crystals and other matter present in the liquid or the spraying equipment.
Conventional methods of removing trapped particles to clean the spray nozzle and allow liquid to flow properly are very labor intensive. The spray nozzles need to be removed frequently from the spraying equipment and cleaned out by hand. Often there are large numbers of spray nozzles and they can be difficult to access locations. The spray nozzles can also be contaminated with toxic or corrosive liquid if that is the nature of the material passing through the nozzle. While this cleaning process is undertaken, production cannot continue which is extremely costly.
In order to reduce the need for frequent cleaning of the nozzles there is disclosed in GB 0987723 a spray nozzle comprising a hollow member having an outlet opening at its front end, and a movable device within the hollow member. The movable device comprises a plurality of separable segmental parts, and the device can be moved by fluid pressure to move the segmental parts towards each other to create a spray discharge orifice at the front end of the nozzle.
The segmental parts can separate when relieved of fluid pressure, so that the discharge orifice can be opened-up for releasing particles so as to tend to prevent collection of matter which could block the orifice.
However, this known spray nozzle has the disadvantage that when orientated so that the open end is lowermost, the segmental parts remain together and fail to release such matter.
There is disclosed in EP 0482369A, a nozzle in which the rear ends of the separable parts have radially outwardly projecting flanges which are engaged by a rear end of a helical compression spring, located in an annular space between the movable device and the hollow member, to thrust the device rearwards away from the open front end of the hollow member. To prevent fluid by-passing the device (by flowing through this annular space), the flanged rear ends carry a packing ring which seals against the internal surface of the hollow member. Additionally, the rear end part of the hollow member is fitted internally with a retaining ring to retain the spring, packing ring and separable parts within the hollow member. In order to force such separable parts to separate when fluid pressure is removed from the nozzle, surfaces of said flanges are inclined so that the spring acts thereon in an attempt to urge apart the front ends of the separable parts, to try to cause the orifice to open when the device is moved rearwards to abut the retaining ring.
The nozzle of EP 0482369A gives rise to more problems than it solves. For example, the spring acts primarily in the axial (front to rear) direction, and thus the packing ring is necessary to ensure that the fluid pressure generates enough force on the device to overcome the thrust of the spring, but a consequence is that (upon the fluid supply being halted) when the device moves rearwards the volume of said annular space increases, sucking in air and/or fluid back into the space at the same time as the separable parts are being separated, with the resultant probability that clogging matter will be drawn into the annular space. Presence of such matter in the annular space, and especially in the slight gap between the flanges and the hollow member, can cause the nozzle to malfunction.
However, the main problem inherent in said nozzle is that it is complex, expensive to make and designed to be replaced as a pre-assembled unit. It is clearly not designed to be dismantled easily for on-site cleaning and would be even more difficult or nearly impossible to reassemble without renewing the rings, thus requiring the user to carry on site stocks of spare nozzles for every spray variant, flow rate and etc type of nozzle employed.
The present invention accepts that some blockages or malfunctions are probably inevitable even with nozzles which are designed to be self-cleaning, and seeks to avoid the problems of manufacturing complexity and spare parts costs.